1. Field of the Invention
The present invention relates generally to Power over Ethernet (PoE) and, more particularly, to a system and method for implementing fairness in the powering of computing devices in a PoE application.
2. Introduction
The IEEE 802.3af and 802.3at PoE specifications provide a framework for delivery of power from power sourcing equipment (PSE) to a powered device (PD) over Ethernet cabling. Various types of PDs exist, including voice over IP (VoIP) phones, wireless LAN access points, Bluetooth access points, network cameras, computing devices, etc.
In the PoE process, a valid device detection is first performed. This detection process identifies whether or not it is connected to a valid device to ensure that power is not applied to non-PoE capable devices. After a valid PD is discovered, the PSE can optionally perform a Layer 1 power classification.
The power requirements of computing devices can vary significantly depending on various factors such as the computing device components, connected devices (e.g., USB devices), application load, etc. These computing devices are typically connected to enterprise networks on a non-permanent basis such as a conference room. In these usage scenarios, a limited power supply would often be oversubscribed as the various computing devices compete for a fixed amount of available power.
The powering of computing devices using PoE in an enterprise environment places a tremendous burden on a switch. For example, in a conference room of ten people with portable computing devices, a switch could require approximately 25 watts per port. This 250 W total can easily approach or exceed the power capacity of the switch. As the number of users connected to the switch increases, the competition for the power resource grows. Various distribution algorithms can be used in these situations to allocate power to the various computing devices. In one example, the distribution algorithm is based on a request priority. One scenario that can arise in this allocation environment is the creation of a starvation condition for certain computing devices. For these computing devices, their power requests could systematically be denied relative to the requests of competing computing devices. What is needed therefore is a mechanism for enabling a PoE system to avoid such starvation conditions.